//定义函数在其他css里面可以直接调用
border-1px($color)
  position relative
  &:after
    display block
    position absolute
    left: 0px
    bottom 0px
    width 100%
    border-top 1px solid $color
    content ' '

//将1像素的横线设置没有
border-none()
  &:after
    display none



bg-image($url)
  background-image url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ration:3),(min-device-pixel-ratio:3)
    background-image url($url + "@3x.png")
